1. Field of the Invention
This invention relates generally to internal combustion engine spark ignition systems, and in particular to an ignition coil module that contains a ferromagnetic core about which primary and secondary coils are coaxially disposed. The ignition coil module may be a type that mounts on an engine over, and in direct electric connection with, an engine-mounted spark plug, in the manner of modules referred to by various names such as pencil-coil modules or coil-on-plug modules.
2. Background Information
Known internal combustion engines comprise cylinder blocks containing individual cylinders that are closed at one end by an engine cylinder head that is attached to the engine block. In a spark-ignition engine, the cylinder head contains threaded spark plugs holes, each of which is open to a respective cylinder. A respective spark plug is threaded into the respective hole to close the respective hole. External to the respective cylinder, each spark plug comprises a central electric terminal that is available for electric connection with a mating terminal of a secondary of the spark-ignition system.
Known spark ignition systems comprise what are sometimes called coil-on-plug type ignition coil modules or pencil-coil modules. Any such module comprises both a wound primary coil and a wound secondary coil. At the proper time in the engine operating cycle for firing a particular spark plug, electric current flowing through the primary of the respective module is abruptly interrupted to induce a voltage in the secondary coil sufficiently high to create a spark across gapped electrodes of the spark plug that are disposed within combustion chamber space of the respective engine cylinder, igniting a combustible fuel-air mixture to power the engine.
Examples of coil-on-plug modules are found in various patents including U.S. Pat. Nos. 4,514,712; 5,128,646; 5,590,637; and 5,870,012; as well as in U.K. Patent Application GB 2,199,193A. A common characteristic of such modules is that the primary and secondary coils are disposed one within the other, concentric with a common axis that is coincident with the spark plug central terminal. The coils may be bobbin-mounted and encapsulated. Various arrangements for providing electric circuit continuity of the secondary coil to the spark plug terminal are shown.
In certain engines, the threaded spark plug mounting hole may be at the bottom of a bore, or well, that extends inward from an outer surface of a cylinder head. For any of various reasons, such bores may be relatively long and narrow, and it is for such bores that pencil-coil ignition modules are especially suited. U.S. Pat. No. 6,094,122 “MECHANICAL LOCKING CONNECTION FOR ELECTRIC TERMINALS”, pending U.S. patent application Ser. No. 09/391,571 “PENCIL IGNITION COIL ASSEMBLY MODULE ENVIRONMENTAL SHIELD”, and pending U.S. patent application Ser. No. 09/392,047 “PENCIL IGNITION COIL ASSEMBLY MODULE” disclose an example of such a module.
An advantage of a pencil-coil module is that when it is installed on an engine, the wiring that runs to it from a signal source need carry only primary coil current, because the entire secondary coil is contained within the module and is for the most part sheltered within the bore. However, for proper ignition system performance, primary and secondary coils must be sized to reliably deliver a secondary voltage sufficiently large to spark the plug. The primary and secondary coils are typically encased in respective encapsulations which must possess physical characteristics suitable for providing protection both for the harsh underhood environment where an ignition coil module is located and for the voltages that must necessarily be generated. Because of dimensional constraints imposed by the design of an engine on a pencil-coil module, it is believed that a module possessing an ability to achieve specified performance criteria within confined space would be valuable to an engine manufacturer. It is further believed that the pencil-coil module shown in U.S. Pat. No. 6,094,122 and the two referenced pending patent applications possesses such value, and that further improvements can increase the value of such a product.